A microalgafrom Chlorarachniaceae was found in the shallow runoffs of south Tehran. Morphological and intracellular structures were studied which in accordance with the identification key (Hirakawa et al. 2011), it is found to be a new species for Iran called Amorphochlora amoebiformis (Ishida & Y. Hara) Ishida, Yabuki & S. Ota. This algahas been derived and evolved from green algae and has resulted from the secondary endosymbiosis of a green alga with an amoeboflagellate. This symbiosis is result of two photosynthetic and amoebic properties appear simultaneously in this species. Having a triangular shape in normal mode with large number of pulsatile filose pseudopodia in the corners of the cell, changing shape from triangular to longitudinal while moving, lack of flagellum, coherent and relatively fast movements, metastatic behavior, twice larger than previous ones dimensions and adaptation to live in shallow runoff, are the characteristics of this alga. Cosmarium, Chlorella and Gleocapsa were companions ofthis species.